A THEORY OF THE FORMATION OF SLIP CHANNELS IN COLD-WORKED BCC METALS

The paper presents a theoretical investigation of microstructural inst abilities in bcc metals that are plastically deformed after previous w ork hardening at low temperatures. Deformation of such materials is, u nder certain conditions, accompanied by a pronounced localization of p lastic strain in narrow slip bands. On the microstructural level, thes e bands correspond to slip channels in which the dislocations caused b y pre-deformation have disappeared almost completely. It is the aim of the present work to formulate the processes which make slip channels emerge from an initially homogeneous dislocation microstructure. To th is end, the interplay between collective dislocation motion and strain softening due to dislocation annihilation is treated in terms of a st ochastic dislocation dynamics. The development of slip channels is pro posed to correspond to a fluctuation-induced phase transition. Critica l conditions for this transition are determined, and the results are c ompared with experimental findings.